The invention relates to a display device being operated in a reflective mode or in a transmissive mode and having pixel elements for modulating light.
Display devices operated in a reflective mode or in a transmissive mode are known. For example, transflective LCD displays are operated in two different modes, i.e. a transmissive mode when the display is lit by a backlight placed behind the display, and a reflective mode when the ambient light lights the display. Transflective LCD displays have the drawback that the display has a limited brightness. This is because the pixel elements of the LCD display are generally divided into reflective and transmissive sections, both of which consequently have a small aperture. At best, a transflective LCD display will only have half the reflectivity of a reflective LCD and half the brightness of a transmissive LCD. Furthermore, a cell gap of the display cannot be simultaneously optimized for both the reflective and the transmissive mode, which further reduces the brightness. In addition, conventional LCD displays use a polarizer, which reduces the intensity of the transmitted light by a factor of two.
It is an object of the invention to provide a display device, which has an improved brightness. To this end, the invention provides a display device as defined in claim 1.
Due to the construction of transflective LCDs, at best only half the pixel surface area of each pixel is involved in reflecting light and the other half is capable of transmitting light. Since use is made of the full pixel surface, a switching display device is inherently two times brighter than a transflective LCD. Such a switching display has an even higher brightness, because no polarizer is required.
Advantageous embodiments of the invention are described in the dependent claims.
Switching mirror displays are known from U.S. Pat. No. 5,905,590. Such a display comprises a switching mirror film including hydrides of gadolinium or other trivalent metals. By exchange of hydrogen, the switching film can be reversibly switched from a transparent state to a mirror-like state with zero transmission via an intermediate black absorbing state. The switching film is comprised in a stack of layers, which is deposited on a transparent substrate. By making a pattern in the switching film and providing the patterned switching film with transparent electrodes, a thin display can be manufactured.
However, U.S. Pat. No. 5,905,590 does not disclose that a transflective display with improved brightness can be provided by applying specific surface charge densities to the switching film.
These and other aspects of the invention will be elucidated with reference to the embodiments described hereinafter.